The invention relates to guidebars for power saws and, in particular, to materials of which such guidebars are constructed.
In power-driven chainsaws, guidebars are used to guide the sawchain laterally and to transmit to the sawchain the feed force needed for the saw teeth to penetrate material being sawed. Guidebars of corresponding design are also used for power-driven saws having one or more reciprocating saw blades.
The drive links of the sawchain or the narrow back of the reciprocating saw blades extend into a groove made in the edge of the guidebar and are laterally guided by the sides of the groove. The edges of the guidebar bordering the groove form smooth rails against which the sawchain or saw blade slides, and which transmit the feed force. The bottom of the groove does not touch the sawchain or saw blade, but serves to transport lubricating oil from oil holes placed near the attachment end of the guidebar.
The guidebar can be made from a thick plate, where the groove at the edge has been made by milling. It is also known that the guidebar can be made as a laminated construction from three thinner plates joined by spot welding. A laminated guidebar presents several technical advantages, including lower vibrations and noise, easier mounting of a nose sprocket and the ability to arrange channels in the middle plate to convey lubricating oil to the nose sprocket. Examples of such laminated guidebars are described in Swedish Patent No. 301,546 and U.S. Pat. No. 3,279,508 (for sawchains) and European Patent No. 212 816 (for saw blades).
In order to reduce wear of the rails at the edge of the guidebar, oil is always supplied, and attempts are made to give the sliding surfaces of the rails great hardness through hardening. This ability is limited, however, since those steel types which are most suitable for hardening cannot be welded with satisfactorily, but rather result in brittle welded joints having numerous micro cracks.
In order to allow use of hardenable alloy steel types for at least the outer plates which form the sliding rails, it has been suggested to join the plates with rubber or glue as in Canadian Patent No. 649,018 or by brazing as in U.S. Pat. Nos. 3,119,418 and 3,545,505, but none of those methods has been shown to give sufficient strength at reasonable cost.
The problem of joining dissimilar materials has been discussed in U.S. Pat. 3,191,646, which in this case recommends riveting, and German Patent No. 35 18 990 which suggests spot welding through small inserts located in holes in the middle plate.